Revert "Fix typo"

This reverts commit 070a850680b3229c366008a4fef76d483dff30e7.
It should not be done by commands.
Revert "Add comment for the reason to introduce restart_worker method"

This reverts commit 3bd4b367ef89c35c323e4663ebcc96ea2b2f67ea.
It should not be done by commands.
Revert "Add codes to restart workers after schema change (WIP)"

This reverts commit 9f03f9a01ba753fea10d92c66a2a8690910d0b68.
It should not be done by commands.